A plantar wart also known as verruca, myrmecia and verruca plantaris[1]:405 is a wart caused by the human papillomavirus (HPV) occurring on the sole (Latin planta) or toes of the foot. HPV infections in other locations are not plantar; see human papillomavirus. Plantar warts are usually self-limiting, but treatment is generally recommended to lessen symptoms (which may include pain), decrease duration, and reduce transmission.[2] Infection occurs in an estimated 7–10% of the US population, and genetics plays an important role in determining susceptibility.

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Plantar warts are benign epithelialtumors generally caused by infection by human papilloma virus types 1, 2, 4, 60, or 63,[3] but have also been caused by types 57,[4] 65,[5] 66,[6] and 156.[7] These types are classified as clinical (visible symptoms). The virus attacks compromised skin through direct contact, entering through possibly tiny cuts and abrasions in the stratum corneum (outermost layer of skin). After infection, warts may not become visible for several weeks or months. Because of pressure on the sole of the foot or finger, the wart is pushed inward and a layer of hard skin may form over the wart. A plantar wart can be painful if left untreated.[2][8]

Warts may spread through autoinoculation, by infecting nearby skin or by infected walking surfaces. They may fuse or develop into clusters called mosaic warts.[3]

A plantar wart is a small lesion that appears on the surface of the skin and typically resembles a cauliflower, with tiny black petechiae (tiny hemorrhages under the skin) in the center. Pinpoint bleeding may occur when these are scratched. Plantar warts often occur on the soles of feet and toes, and can occur on hands and fingers. When they occur on feet they may be painful when standing or walking.

Plantar warts are often similar to calluses or corns, but can be differentiated by close observation of skin striations. Feet are covered in skin striae, which are akin to fingerprints on the feet. Skin striae go around plantar warts; if the lesion is not a plantar wart, the striations continue across the top layer of the skin. Plantar warts tend to be painful on application of pressure from either side of the lesion rather than direct pressure, unlike calluses (which tend to be painful on direct pressure instead).

HPV is spread by direct and indirect contact from an infected host. Avoiding direct contact with infected surfaces such as communal changing rooms and shower floors and benches, avoiding sharing of shoes and socks and avoiding contact with warts on other parts of the body and on the bodies of others may help reduce the spread of infection. Infection is less common among adults than children.[8]

As all warts are contagious, precautions should be taken to avoid spreading them. The British National Health Service recommends that children with warts:

Plantar warts are not prevented by inoculation with currently available HPV vaccines, because the warts are caused by different strains of the human papillomavirus. Gardasil protects against strains 6, 11, 16, and 18; and Cervarix protects against 16 and 18; whereas plantar warts are caused by strains 1, 2, 4, and 63.

Cantharadin (blister beetle extract) applied to a wart by a doctor causes a blister after 4–6 hours. One formulation is known as Cantharone (0.7% Cantharidin); a more powerful one is Cantharone PLUS which contains the same active ingredient as Cantharone, but it also contains Podophyllin (5%) and Salicylic Acid (30%).

A ~7mm plantar wart surgically removed from patient's footsole after other treatments failed

Liquid nitrogen—This, and similar cryosurgery methods, is a common surgical treatment which act by freezing the internal cell structure of the warts, destroying the live tissue. Up to three sessions may be required.

Laser surgery—This is generally a last resort treatment, as it is expensive and painful, but may be necessary for large, hard-to-cure warts.[13]

Cauterization—This may be effective as a prolonged treatment. As a short-term treatment, cauterization of the base with anaesthetic can be effective, but this method risks scars or keloids. Subsequent surgical removal is unnecessary, and risks keloids and recurrence in the operative scar.[14]